They vanish, seemingly without a trace, leaving their friends and family panicking about what could have happened.

Have they been abducted? Murdered? Are they lying injured in a ditch somewhere? Could they have committed suicide or have they just taken off, not wanting to be found.

These are the sorts of questions officers in the Missing Persons Unit grapple with on a daily basis.

National Missing Persons Week has been officially launched today, to recognise missing people who have been found, to remember those who are still lost and to gather information to bring them home.

In New South Wales alone there are more than 200 calls a week. Most are solved easily but each one needs to be taken seriously. There are 35,000 people reported missing each year.

SOMEONE DISAPPEARS. WHAT SHOULD YOU DO?

Sergeant Cath Borton told news.com.au the first few hours someone was missing were valuable and it was important to gather as much information as possible.

One of the biggest misconceptions about missing people was you had to wait 24 hours to report someone missing.

Katrina Bohnenkamp. She was last seen at her home address in Greenacre, NSW, in October 2012. At the time Katrina left the house she did not say where she was going or what time she would return.Source:Supplied

It’s something probably gleaned from US crime shows but was a myth, Sergeant Borton said.

When the missing persons report is made the investigating officers will be on the lookout for anything suspicious, unusual or out-of-character that could explain why someone is not where they should be.

Firstly it will be the mundane but necessary details — and here is often where there will be a vital clue.

“We record the date/time/location the person was last seen … Their full details, name, date of birth and description of what they were wearing.”

Their mobile phone number, their bank account details and their friends were all recorded.

Having a recent picture of the person was important too and it had to be a proper likeness of the person and “not a glam shot”, Sgt Borton said.

In this age of the 24-hour media cycle and rampant social media, police will also get family members written permission to distribute the picture to media, which can be crucial in getting the message quickly to a large number.

Douglas Allan was last seen at his aged care facility in Wyoming, NSW on the 12 September 2009.Source:Supplied

THE SEARCH BEGINS

One of the most important tasks is risk assessment, which is either high, medium or low. It isn’t an exact science but it can give police an early guide as to why someone has disappeared. Was it of their own accord or is there foul play involved?

During this assessment police take into consideration who is reporting the person missing. For example, a parent who knew their child’s movements well carried more weight than someone who wasn’t familiar with their routine, like a neighbour.

Also important is everything from their mental health and domestic situation and are “all taken into consideration”. As is any note they could have left.

Despite that, Sgt Borton said the action taken by police was still the same, and they would begin with calling the person’s mobile and speaking to their friends.

Megan Louise Mulquiney. Megan was last seen inside a shopping centre about 12.15pm and was supposed to catch a bus home. But she never arrived. Her family said she was a responsible person and would always contact them if her plans changed.Source:Supplied

Margaret Anne Bernie was last seen on 26 January 1988 in South Australia.Source:Supplied

THE NUMBERS

Across Australia the number of missing persons reported each year is 35,000 but the percentage of people who reappear quickly is very high. Sergeant Borton said year after year 99 per cent are located.

A breakdown of the New South Wales’ missing person reports showed there were 679 long-term cases — people missing more than a year — with the oldest dating back to 1945.

Last year in NSW there were 11.805 people reported missing. But of those 11, 797 were located.

So while the vast majority do turn up that is of little comfort to the families of the small number who are never heard from again.

An emerging trend Sgt Borton and her colleagues at the Missing Persons Unit have noticed is the increasing number of older people being reported missing. Ten per cent of the calls are now for people aged 60 or older. But the vast majority — 60 per cent — are teenage runaways.

Sgt Borton said people suffering dementia was something her unit saw regularly and because of this Missing Persons Week this year, which begins today, has partnered with Alzheimer’s Australia in an attempt at boosting awareness of the issue.

Marie Dorothy Agostino was last seen at her home address in Footscray on 13 March 1984 when she said she was going for a walk for an hour. She never returned, leaving two young sons.Source:Supplied

THE FAMILIES

“It’s awful for the families,” Sgt Borton said. What’s important though is keeping them informed — even if there was very little to say — because even a phone call to let them know they hadn’t been forgotten could be reassuring.

If someone was still missing after three months DNA was collected from the family which could be tested against bodies that hadn’t been identified.

Sgt Borton said officers developed a relationship with the families, especially with some of the longer term missing, in which case the contact was regular, and ongoing.

It was because of this investigators gained an emotional attachment and never treated their subjects like a “run of the mill file”.

“You never take it for granted.”

Qing Yue Chen was last seen on 24 October 2000 at Dulwich Hill.Source:Supplied

THE MISSING — AND THEIR SECRETS

Each day was different and just when she thought she’d seen and heard everything, something they hadn’t seen before would come across their desk.

With more than 200 calls a week, it’s hardly surprising.

To get to the bottom of a mystery you need to delve into a person’s life. That means intimate details of their lives, and secrets, are laid bare.

“Sometimes families don’t want to find out.”

There can be depression, alcoholism, relationship breakdowns, including affairs. That all comes out of the woodwork.

It seems while people wanted their loved ones found, knowing what was going on in their lives can be confronting.

In these cases police have to be tactful and tread carefully, especially in the early days when they need the family’s co-operation. This is particularly important when the missing persons case could still turn out to be homicide.

Michael Devitt, missing from Queensland since February 2010.

THE SEARCH GOES ON

When a person was not immediately found, a case file didn’t just sit in a cabinet gathering dust and the missing person forgotten about.

Each one was regularly reviewed with “fresh pair of eyes” over it “end to end”, Sgt Borton said.

Like all areas of police work, personal connections were made with the family and friends of those of the lost.

Instead Sgt Borton said her team tried to devise ways of finding people and returning them to their loved ones. Or at least provide them with an explanation and give them closure.

“You think of doing [the investigation] different ways, thinking outside of the square ... To find out what has happened to these people.”

Eve Askew. Run away from her home at Fitzgerald, Tasmania in November 1991 after being grounded for smoking. There has been no contact since her disappearance. Since she has been gone Eve is unaware that her parents have both since died, and she has become an Aunt.